NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Thermal Performance 

Benchmarking

Gilbert Moreno

Organization: NREL

Email: Gilbert.Moreno@nrel.gov

Phone: 303-275-4450

Team members/collaborators: Kevin Bennion (NREL), Tim Burress (ORNL)

DOE Vehicle Technologies Office

Electric Drive Technologies

FY15 Kickoff Meeting

Oak Ridge National Laboratory

Oak Ridge, Tennessee

November 18 – 20, 2014 This presentation does not contain any 

proprietary or confidential information.

NREL/PR-5400-63001
2

State-of-the-Art Thermal Management 

Systems

Power electronics thermal management

• Cast aluminum, serpentine channel 

heat exchangers

• Double-side cooling of power modules

Electric motor thermal management

• Liquid (water-ethylene glycol)-cooled 

stator jacket

• Automatic transmission fluid-cooled endwindings

DOE APEEM FY15 Kickoff Meeting

2012 Nissan Leaf

2013 Toyota Camry

2012 Nissan Leaf

(Credit: Kevin Bennion, NREL)

(Credit: Gilbert Moreno, NREL)

Image courtesy of ORNL
3

Proposed Technology 

Strategy to Address Limitations of SOA

DOE APEEM FY15 Kickoff Meeting

• Provide insight into various thermal management 

technologies

• Identify areas of improvement to advance thermal 

management SOA

• Complement Oak Ridge National Laboratory’s 

(ORNL’s) benchmarking of power electronics and 

electric motors project, but only focus on the 

thermal management technologies
4

Challenges/Barriers to Meet Project Goals

DOE APEEM FY15 Kickoff Meeting

• Obtaining the vehicle components may 

be an issue

• Experiments may not exactly replicate 

the actual automotive environments or 

operating conditions
5

Project Approach: Objectives and Motivation

DOE APEEM FY15 Kickoff Meeting

Overall objective: To benchmark the thermal characteristics of the power 

electronics and electric motor thermal management systems

• Establish baseline metrics for the thermal management systems 

• Evaluate advantages and disadvantages of different thermal management 

systems

• Identify areas of improvement to advance the SOA

FY15 objective: Benchmark the 2012 Nissan Leaf power electronics and motor 

thermal management systems

• ORNL benchmarked the electrical aspects of the 2012 Nissan Leaf in 2013

Motivation: Help industry to reduce the weight, volume, and cost of vehicle 

traction-drive systems by providing information that may influence future product 

designs; also help guide future APEEM R&D efforts
6

Project Approach: Overview

DOE APEEM FY15 Kickoff Meeting

Collaborate with industry and ORNL to identify the 

vehicle system to benchmark

Acquire the vehicle components

Measure the characteristics of the thermal 

management systems

- Experimentally measure thermal performance metrics

- Utilize modeling, particle image velocimetry, high speed video, 

and infrared imaging to understand heat transfer mechanisms

Analyze the data and calculate thermal 

performance metrics

Share results with industry and research institutions
7

Project Approach: Thermal Measurements 

DOE APEEM FY15 Kickoff Meeting

Electric motor thermal 

management

• Winding-to-liquid thermal 

resistance

• Motor lamination and 

winding thermal properties

• Pressure drop through the 

heat exchanger

• Volume and weight of the 

heat exchanger

Power electronics thermal 

management

• Junction-to-liquid thermal resistance

• Interface material thermal resistance

• Capacitor thermal properties

• Thermal resistance and pressure 

drop through the heat exchanger

• Volume and weight of the heat 

exchanger

Thermal management components

• Pump pressure versus flow rate characteristics and efficiency

• Radiator thermal resistance and liquid- and air-side pressure 

drop 

(Credit: Gilbert Moreno, NREL)

(Credit: Kevin Bennion, NREL)

(Credit: Scot Waye, NREL)
8

Project Approach: NREL Lab Facilities Utilized 

Water–ethylene glycol 

(WEG) test bench

Automatic transmission 

fluid test bench

Transient thermal tester 

(T3ster)

Particle image 

velocimetry, high-speed 

video, and infrared 

imaging cameras

Air-cooling test bench

ASTM thermal interface 

material (TIM) test bench

DOE APEEM FY15 Kickoff Meeting

(Credit: Gilbert Moreno, NREL) (Credit: Scot Waye, NREL) (Credit: Kevin Bennion, NREL)

(Credit: Kevin Bennion, NREL)

(Credit: Justin Cousineau, NREL)
9

FY15 Tasks to Achieve Key Deliverable

DOE APEEM FY15 Kickoff Meeting

2014

Oct Nov Dec

2015

Jan Feb Mar Apr May Jun Jul Aug Sep

Go / No-Go Decision Point: Determine if a vehicle system is available and relevant for 

benchmarking

Key Deliverable: A year-end report describing the thermal characteristics of the 

2012 Nissan Leaf power electronics and motor thermal 

management systems 

Test inverter thermal 

management system

Test motor thermal 

management system

Test radiator and pump

Go/

No-Go 

Decision 

Point

Key 

deliverable: 

Year-end 

report
10

2012 Nissan Leaf Traction-Drive Thermal Management 

System

Inverter thermal 

management system

Electric motor thermal 

management system

Cooling system components (radiator and pump)

DOE APEEM FY15 Kickoff Meeting

(Credit: Kevin Bennion, NREL)

(Credit: Scot Waye, NREL)
11

Inverter Thermal Management System 

Tests

• Power modules are attached 

to an aluminum cold plate

• Devices are bonded to a 

copper-molybdenum plate 

that helps to spread heat but 

leaves the backside of the 

modules electrically active

• Dielectric insulator is 

provided to electrically 

isolate the modules

Measure the thermal resistance 

•total resistance (junction-to-liquid),

• passive stack resistance (junction-to-case).

Measure the TIM 

thermal resistance

Measure the 

dielectric insulator 

thermal resistance

DOE APEEM FY15 Kickoff Meeting

(Credit: Scot Waye, NREL)

Measure the capacitor thermal conductivity
12

Inverter Thermal Management System 

Tests

• Serpentine channel-type heat exchanger that uses WEG

Measure the cold plate 

thermal resistance

Measure the 

coolant pressure 

drop

DOE APEEM FY15 Kickoff Meeting

Image courtesy of ORNL
13

Motor Thermal Management System

• Motor is cooled with an aluminum cooling jacket that surrounds 

the stator

• WEG is circulated through the cooling jacket channels

Liquid cooling 

WEG inlet jacket

WEG outlet Measure the total thermal 

resistance (winding-to-liquid)

Measure the coolant pressure drop

DOE APEEM FY15 Kickoff Meeting

(Credit: Kevin Bennion, NREL) (Credit: Kevin Bennion, NREL)
14

Motor Thermal Management System Tests

• Circulate WEG through the 

cooling jacket

• Heat the windings by running a 

high current (low voltage) 

through each of the phases

• Measure the end-winding 

temperature using 

thermocouples, copper electrical 

resistance measurements, 

and/or infrared imaging

Thermal image of motor with 

single phase heated

Thermal image of motor with 

all phases heated

DOE APEEM FY15 Kickoff Meeting

(Credit: Kevin Bennion, NREL)

(Credit: Kevin Bennion, NREL)
15

Motor Thermal Management System Tests

Motor passive-stack thermal properties

• Measure the effective thermal conductivity and heat capacity

Measure the stator 

lamination effective 

thermal conductivity 

and specific heat

Measure the endand slot-winding 

effective thermal 

conductivity and 

specific heat

DOE APEEM FY15 Kickoff Meeting

(Credit: Kevin Bennion, NREL)
16

System Component Tests

Radiator

• Air-to-liquid thermal resistance (at various air-flow rates)

• Air- and liquid-side pressure drops

• Volume and weight

Coolant pump

• Pressure versus flow rate

• Efficiency versus flow rate

• Volume and weight

Flow rate

Pressure

Efficiency

DOE APEEM FY15 Kickoff Meeting
17

Calculate System Thermal Metrics

Measure:

• Component (inverter, motor, radiator) and total (junction-to-air, 

winding-to-air) thermal resistances

• Total parasitic power

• Total volume and weight

Compute:

• System coefficient-of-performance

• Thermal power density

• Thermal specific weight

Identify thermal bottlenecks and propose strategies to improve 

thermal management

DOE APEEM FY15 Kickoff Meeting
18

FY16 Task Description

• Benchmark the thermal characteristics of the 2014 Honda Accord 

(hybrid) inverter and electric motor thermal management systems

Collaborate with industry and ORNL to identify the vehicle 

system to benchmark

Acquire the vehicle components

Measure the characteristics of the thermal 

management systems

- Experimentally measure thermal performance metrics

- Utilize modeling, particle image velocimetry, high-speed video, 

and infrared imaging to understand heat transfer mechanisms

Analyze the data and calculate thermal performance 

metrics

Share results with industry and research institutions

DOE APEEM FY15 Kickoff Meeting
19

FY16 Tasks to Achieve Key Deliverable

DOE APEEM FY15 Kickoff Meeting

Go / No-Go Decision Point: Determine if a vehicle system is available and relevant for 

benchmarking

Key Deliverable: A year-end report describing the thermal characteristics of the 

2014 Honda Accord Hybrid power electronics and motor thermal 

management systems

2015

Oct Nov Dec

2016

Jan Feb Mar Apr May Jun Jul Aug Sep

Test inverter thermal 

management system

Test motor thermal 

management system

Test radiator and pump

Go /

No-Go 

Decision 

Point

Key 

deliverable: 

Year-end 

report
20

FY17 Task Description

• Vehicle system to be benchmarked remains to be identified

Collaborate with industry and ORNL to identify the 

vehicle system to benchmark

Acquire the vehicle components

Measure the characteristics of the thermal 

management systems

- Experimentally measure thermal performance metrics

- Utilize modeling, particle image velocimetry, high-speed video, and 

infrared imaging to understand heat transfer mechanisms

Analyze the data and calculate thermal performance 

metrics

Share results with industry and research institutions

DOE APEEM FY15 Kickoff Meeting
21

FY17 Tasks to Achieve Key Deliverable

DOE APEEM FY15 Kickoff Meeting

Go / No-Go Decision Point: Determine if a vehicle system is available and relevant for 

benchmarking

Key Deliverable: A year-end report

2016

Oct Nov Dec

2017

Jan Feb Mar Apr May Jun Jul Aug Sep

Test inverter thermal 

management system

Test motor thermal 

management system

Test radiator and pump

Go /

No-Go 

Decision 

Point

Key 

deliverable: 

Year-end 

report
22

Project Summary

DOE APEEM FY15 Kickoff Meeting

Project Duration: FY15 – FY17

Overall Objective (all years): Benchmark the thermal characteristics of the power 

electronics and motor thermal management systems

FY15 Focus: Benchmark the 2012 Nissan Leaf thermal management systems

Deliverable: Year-end report detailing the performance of the 2012 Nissan Leaf power electronics and 

motor thermal management systems

Go/No-Go Decision Point: Determine if a vehicle system is available and relevant for benchmarking

FY16 Focus: Benchmark the 2014 Honda Accord Hybrid thermal management systems

Deliverable: Year-end report detailing the performance of the 2014 Honda Accord Hybrid power 

electronics and motor thermal management systems

Go/No-Go Decision Point: Determine if a vehicle system is available and relevant for benchmarking

FY17 Focus: Benchmark the performance of a vehicle’s thermal management systems

Deliverable: Year-end report

Go/No-Go Decision Point: Determine if a vehicle system is available and relevant for benchmarking
23

Technology-to-Market Plan

DOE APEEM FY15 Kickoff Meeting

• Results from these benchmarking studies 

will be a resource to industry and may 

influence future industry product designs 

• Help guide future APEEM R&D efforts
24

Partners/Collaborators

DOE APEEM FY15 Kickoff Meeting

Organization Role

Oak Ridge National 

Laboratory

• Benchmark the packaging, 

materials, and electrical 

performance aspects of 

the power electronics and 

electric motor(s)

• Consulted on thermal 

benchmarking activities
For more information, contact:

Principal Investigator

Gilbert Moreno

Gilbert.Moreno@nrel.gov

Phone: (303) 275-4450

APEEM Task Leader:

Sreekant Narumanchi

Sreekant.Narumanchi@nrel.gov 

Phone: (303) 275-4062

Acknowledgments:

Susan Rogers and Steven Boyd

U.S. Department of Energy

Team Members:

Kevin Bennion (NREL)

Tim Burress (ORNL)